The 21-year-old accepted the punishment - believed to be around ?120,000 - after being pictured outside a strip club in Liverpool in the early hours of Friday morning, contravening club regulations ahead of Saturday's game against Bolton.
Balotelli went on to play and score in the Barclays Premier League leaders' 2-0 defeat of the Trotters at the Etihad Stadium and Mancini said: "I spoke with Mario and gave him a fine of one week's wages for what he did. This is normal because every player should have good behaviour before the game."
When asked if Balotelli had accepted the fine, Mancini said: "Yes."
It is the second time Balotelli has broken a curfew this season - among a host of other high-profile misdemeanours - but he admitted in an interview published yesterday that he had made a mistake.
Mancini was speaking in Portugal ahead of the first leg of City's Europa League last-16 tie against Sporting Lisbon at the Jose Alvalade on Thursday. The Italian dismissed suggestions from the Portuguese side that the club may underestimate the challenge ahead of them.
City thrashed Portuguese champions Porto 6-1 on aggregate in the previous round but Mancini insists there will be no complacency as they come up against a lower-ranked side.
Sporting are currently fourth in the Portuguese league, 14 points behind Porto, and suffered a shock loss to struggling Setubal at the weekend.
Mancini said: "I played here five years ago with Inter in the Champions League and we lost. We had the same situation the day before. I don't think an easy game exists in football, in the Europa League. Every game is very difficult.
"If we want to win tomorrow we should play very well and have good concentration for this game. Sporting Lisbon are a good team and play very good football."